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How OWTSs Using Aerobic Treatment Work. Texas AgriLife Extension Sevice. Overview. Treatment Processes Components of an OWTS using Aerobic Treatment, Disinfection and Spray Dispersal What is a Flow Equalization Tank?. Aerobic Treatment Unit System. Wastewater Treatment Processes.

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how owtss using aerobic treatment work

How OWTSs Using Aerobic Treatment Work

Texas AgriLife Extension Sevice

overview
Overview
  • Treatment Processes
  • Components of an OWTS using Aerobic Treatment, Disinfection and Spray Dispersal
  • What is a Flow Equalization Tank?
wastewater treatment processes
Wastewater Treatment Processes
  • Oxygen state
    • Aerobic vs. Anaerobic
  • Processes
    • Physical
    • Chemical
    • Biological
aerobic vs anaerobic processes
Aerobic vs. Anaerobic Processes (???)
  • Aerobic
    • Aerobic bacteria require O2 to live and grow
    • Aerobic treatment processes require O2 to proceed
    • Common condition in soil treatment, media filters, MATUs
  • Anaerobic
    • Anaerobic bacteria grow in absence of free oxygen,O2
    • Anaerobic treatment processes do not use oxygen, but consumption of items, breaks oxygen bonds Ex. SO4, NO3
    • Common condition in septic tanks, processing tanks, and usually any saturated environment
slide7

Large Rotifers Attached to Aerobic Treatment Media Feeding on Bacteria & Organic Nutrients pH 6.94, DO 4.54 ppm

atu disinfection and spray distribution system components
ATU, Disinfection and Spray Distribution System Components
  • Septic/Trash tank
  • Aerobic Treatment
  • Air Supply
  • Clarification
  • Sludge Return
  • Disinfection
  • Pump tank with pump and controls
  • Spray field
septic trash tanks
Septic/Trash Tanks
  • Most common treatment system:
    • Water tight tanks.
    • Anaerobic Treatment.
    • Most common treatment device.
    • Septic tank: Minimum of two compartments
    • Trash tank: Typically smaller with one compartment
  • Some systems do not have a trash tank.
septic tank treatment process
Septic Tank Treatment Process
  • Physical separation processes –
    • Settling of heavy materials – sludge layer
    • Floating of lighter materials – scum layer
    • Clear zone (clear layer)
    • Effluent screen to assist in trapping solids (septic tank)
  • Time is the main requirement to allow separation to occur
    • Detention time:
      • Septic tank - 2-3 days
      • Trash tank – 1 day
    • Distance between inlet/outlet baffles is critical
  • Calm conditions to prevent mixing in the tank
  • Anaerobic digestion and storage of materials until the tank is pumped
aerobic treatment

Aerobic Treatment

Aeration Chamber

aerobic treatment process
Aerobic Treatment Process
  • Aerobic microbes digest solids
    • Organic matter + O2 = CO2 + H2O + new cells
  • Sludge accumulates in tank
  • Extended aeration
    • High DO, Long detention, Low Food/Microorganisms ratio
    • Organic matter to microbes, microbes eat each other, result in sludge
suspended growth
Suspended Growth
  • Aerobic microbes free swimming in the aeration chamber
  • Mixing in the chamber mixes the microbes and the wastewater contaminants
  • Extended aeration to limit biomass wasting
submerged attached growth fixed film media
Submerged Attached Growth/Fixed Film Media
  • Media is submerged in the aeration chamber
  • Microbes are attached to the media
  • Effluent is circulated through the media thus passing contaminants by the microbes
  • Extended aeration to limit biomass wasting
suspended growth configurations
Suspended Growth Configurations
  • Should be three chambers/tanks.
  • Single tank with three compartments.
  • Multiple tanks.
  • May combine aeration and clarification chamber with divider
attached growth configurations
Attached Growth Configurations
  • Most have three chambers
  • May be a separate media filled insert
  • May have media placed in the aeration chamber
  • Check manufacturer literature
aeration of wastewater
Aeration of Wastewater
  • Air is 21% oxygen
  • Oxygen must transfer to wastewater for DO
  • Quantity of oxygen transferred directly related to BOD removal
  • Mixing of sewage
aspirator aerator
Aspirator/Aerator
  • Vacuum pulls air into the water
  • Spinning shaft or impeller causes the vacuum
  • Limited resistance
compressors
Compressors
  • Greater pressure
  • Lower air flow
  • Two distinct types of compressors
    • Rotary
    • Linear
  • Air inlet
  • Housing - cover

Rotary

Linear

compressor air flow
Compressor Air Flow

Rotary

  • Rotary compressor - Relatively straight increase in flow with a decrease in pressure
  • Linear compressor – rapid decrease with increasing pressure
    • Flow drops with resistance to air flow
  • Must have the correct compressor to have the correct air flow

Linear

blowers
Blowers
  • Greater air flow
  • Lower pressure
  • Air inlet screens/filters
  • Air flow discharge from unit
  • Larger pipe
  • Air flow stops sharply
  • Cannot operate under higher pressure
air distribution lines
Air Distribution Lines
  • Minimize friction loss in the distribution lines:
  • Proper pipe diameter
  • Reasonable distance between aerator and aeration chamber
  • Minimize number of fittings (changes in direction) in the line.
air diffusion
Air Diffusion

Perforated Pipe

Porous Stone Diffuser

clarification1
Clarification
  • Process occurs in a “clarifier”
  • Clarification is the process were the microbes, cell waste and biomass settle out of the water.
  • Sludge blanket in the bottom and a clear zone below the discharge point
vertical settling chamber
Vertical Settling Chamber
  • Calm Environment
  • Particles of Sufficient size and mass to settle
  • Flow dependent
  • Upward flow rate must be less than the settling rate

V = Q/ A

configurations
Configurations
  • Separate chamber with no extra filtration
  • Cone inserted into aeration chamber
  • Many have sloped walls
  • Added tertiary filter or screen in clarifier
  • Filtration through socks placed in the aeration chamber
  • Added filtration improves quality but increases maintenance
controlling flow from a residence
Controlling Flow from a Residence
  • Owner controls water usage to match clarifier capacity
  • No large water using devices
  • 500 gpd ATU has a max of 42 gph without flow equalization
  • Or Install larger capacity system
flow equalization surge tank concepts
Flow Equalization/Surge Tank Concepts
  • Moderate Flow
    • Daily fluctuations
    • Weekly fluctuations
  • Down stream components
    • Function more effectively
    • May allow decrease size
  • Timer controls dosing to ATU
flow equalization surge tank
Flow Equalization/Surge Tank

Sized based on Peak Flow

incorporating flow equalization
Incorporating Flow Equalization
  • Modify the treatment train by adding components
  • Add an additional tank between the trash tank and aeration chamber
  • Upsize trash tank to full size septic tank, add pump with timer controls to dose ATU
sludge return1
Sludge return
  • Settled solids passing into a previous treatment chamber
  • Passive system
    • Settled solids passing through the bottom opening
    • Most common method
  • Active system
    • Settled solids blanket below the outlet baffle
slide41

Disinfection,

not Sterilization

The goal of disinfection

is to rid the wastewater stream

of organisms capable of causing infection

Sterilization is freeing

the wastewater stream of ALL LIFE.

slide42

Chlorine

  • Destroys target organisms by chemical oxidation of cellular material.
  • Some organisms are resistant to low doses of chlorine
    • Oocysts of Chrytosporidium parvum
    • Cysts of Endamoeba histolytica
    • Cysts of Giardia lamblia
    • Eggs of parasitic worms
chlorination considerations
Chlorination Considerations
  • Chlorine is an oxidizer.
  • Need clean water (low BOD, low TSS): chlorine is not “stolen” to oxidize organic matter.
  • Chlorine reacts with ammonia to form chloramines.
  • Chloramines are not as effective as hypochlorous acid and hypochlorite ion for disinfection.
  • Interferences: BOD, TSS, Humic Materials, Nitrite, pH, Iron, manganese and hydrogen sulfide
dosing
Dosing

Dose = Concentration x Time

  • Increasing either dosage or contact time, while decreasing the other, can achieve the same degree of disinfection.
  • Breakpoint- the process where sufficient chlorine is added to the system to obtain a free chlorine residual
caution
Caution
  • People should be trained to properly handle and work with chlorine products
  • High risk
    • Exposure
    • Handling
  • Corrosive
  • Unstable
  • Be careful where stored!!!!!!
tablet chlorination
Tablet Chlorination
  • Tablet chlorinators generally have four components:
    • Chlorine Tablets.
    • A tube that holds the tablets.
    • A contact device, which puts the chlorine tablets into contact with the wastewater.
    • A storage reservoir, usually a pump tank where the water is stored before it is distributed.
typical chlorine tablets
Typical Chlorine Tablets
  • Wastewater tablets- Calcium Hypochlorite
    • Basic compound – high pH
  • Swimming pool – Trichlorocyanuric acid
    • Acidic compound – low pH
  • Hazard to mix acids and bases
  • Must use products in accordance with label
residential liquid bleach chlorinator
Residential Liquid Bleach Chlorinator
  • Reservoir
  • Delivery of chlorine
    • Vacuum/suction
    • Pump
  • Dose volume
  • Mixing with effluent
residential liquid chlorination
Residential Liquid Chlorination
  • Flow passes through aspirator developing a vacuum or through a pump to draw a dose of chlorine.
  • Tubing delivers chlorine dose to aspirator or pump
  • Control volume of chlorine
  • Mixing of chlorine with effluent in pump tank
ultraviolet light disinfection units
Ultraviolet Light Disinfection Units
  • UV light destroys microorganisms by altering their genetic material and / or retarding their ability to reproduce
ultraviolet light disinfection units1
Ultraviolet Light Disinfection Units
  • Electromagnetic energy (UV light) from source lamp is emitted into a chamber through which effluent passes
other interferences to effective uv disinfection
Other Interferences to Effective UV Disinfection
  • Dissolved organic compounds (BOD, TOC, COD)
  • Organic iron compounds
  • Humic compounds (tannins)
  • Inorganic coatings on protective tubes
pump tank pump
Pump Tank & Pump
  • Stores water until time for dosing effluent
  • Acts as storage for disinfection
  • Storage capacity when system breaks
  • Pump
    • Type: effluent or sewage
    • Not a grinder or sump
    • Specific flow & pressure
panel electrical control circuits
Panel & Electrical Control Circuits
  • Panel is a housing for components needed to control a system.
  • Record valuable operational information
  • Provide a means to collect operational data on the system
  • Timer for night spray
  • Timer for flow equalization
  • Audio and visual alarms
  • Power must be ON!
spray field1
Spray Field
  • Lawn Sprinkler systems? --- NO!!!
  • Spray treated wastewater over the surface of a yard
  • Requires greatest level of treatment
  • High risk system!!!!
water quality
Water Quality
  • High potential for human contact with water
  • Secondary- Quality Effluent
  • Remove 85-98% of solids and organic matter
  • Remove pathogens?
  • Nutrients (nitrogen and phosphorus) are not required to be removed
  • Soil for Final Treatment

No Playing in Sprinklers

role of vegetative cover in treatment system
Role of vegetative cover in treatment system
  • A healthy cover crop is essential for the system to function properly. Plants will:
    • Take up nutrients
    • Take up water
    • Stabilize the soil and prevent erosion
    • Provide food and habitat for beneficial soil organisms
  • Soil microbes are the final treatment!!!!
    • This is effluent – NOT DRINKING WATER!!!!
summary
Summary
  • Treatment requirements
  • Components of an OWTS using Aerobic Treatment, Disinfection and Spray Dispersal
  • What is a Flow Equalization Tank?